April 18, 2018


The Strateole 2 project aims to observe the equatorial higher troposphere and lower stratosphere using superpressure balloons capable of staying aloft for several months.

What’s needed to better predict climate

To predict climate better, we first need to understand the mechanisms underlying transport of water vapour from the troposphere to the stratosphere, driven by large-scale convective motions associated with cloud masses in equatorial regions, and to learn more about atmospheric undulations in these regions, especially those generated by these powerful convective systems.

Strateole 2 will deliver data on key parameters driving the dynamic and physical processes affecting climate in the tropics, as well as at global scale as far as the polar regions.

Strateole 2 is a valuable addition to existing observation assets, providing measurements at high spatial and temporal resolution to effectively complement data acquired at fixed points on the ground and at fixed but not very frequent times from space-based instruments.

What Strateole 2 will do

Unprecedented tracking of air masses

  • The balloon drifts for several months at a near-constant level where the density of the air is equal to its own density, which doesn’t vary. This means it operates as a ‘quasi-Lagrangian’ system, as it is able to track the mass of air in which it is floating for a long period.

    The ability of such ultra-long-duration (ULD) flights to remain aloft at a constant level in the lower atmosphere is down to a series of mature technologies conferring a very high level of airtightness and great mechanical strength to the balloon, and to its reliability, lightness and power autonomy and the aptitude of the control systems to communicate effectively with the control centre.

  • The balloon drifts slowly in the stratosphere at the same speed as the mass of air in which it is floating, thus affording high spatial and temporal resolution to observe a situation or atmospheric phenomenon in fine detail and obtain measurements in close succession to track how they vary over a day/night cycle.

    Flying a flotilla of balloons also makes it possible to observe a great diversity of situations across the globe, and sometimes simultaneously with a satellite or ground-based asset. Measurements from superpressure balloons are thus a very useful complement to other observing systems.

Instrument expertise

A suite of scientific instruments has been developed to measure the atmospheric characteristics on which the mission is focused. Some of these acquire measurements in situ, from the air surrounding the balloon, for example concentrations of water vapour, ozone and carbon dioxide, detecting the presence of ice in suspension or measuring air temperature and pressure with high sensitivity. Other instruments sound the balloon’s environment, out to several kilometres using lidar or by deploying sensors underneath the balloon, or to several hundred kilometres by radio-occultation of navigation satellite signals. All of these instruments designed to tight mass and power specifications must be adapted to the environment of the lower stratosphere, where air pressure and temperature are extremely low (–85°C).

Calibrating and validating space-based atmospheric instruments

Data collected during Strateole 2 will help notably to validate lidar measurements acquired for the first time from space by the European Space Agency’s Aeolus satellite.

Links with atmosphere models

  • Strateole 2 is measuring physical and dynamic processes in the tropopause—the interface between the troposphere and the tropical stratosphere—to study and characterize phenomena that are still poorly understood, such as wave mechanisms, the impact of the most powerful convective systems, water transport from the troposphere to the stratosphere, the formation of high-altitude cirrus clouds and winds in the lower tropical stratosphere.
  • Strateole 2 will help to analyse and model these processes in order to refine the climate models used by climate prediction centres.
  • Strateole 2 will also help to provide near-real-time (within one hour) observations of the atmosphere for use by weather forecasting centres, enabling them to improve weather forecasts in the tropics and global numerical weather prediction models.

Strateole 2 - Around the world in 84 days

Following in the footsteps of Jules Verne, the superpressure balloons will observe for three months on average the mechanisms driving the formation of high clouds and the composition of the atmospheric layers of the equatorial zone: the troposphere and stratosphere, and more specifically the boundary between the two, the tropopause.

The project will also investigate the east-west cycles of the Quasi-Biennial Oscillation (QBO), a change in the direction of stratospheric winds at the equator which follows a cycle of 28 months or so on average. Strateole 2 will help to better understand and predict this phenomenon.

Safety and sovereignty of nations overflown

The balloons could overfly up to 77 countries. In accordance with the rules of national sovereignty, the prior consent of these nations is sought. The safety of populations on the ground is a constant concern. A set of rules is defined and their application checked by a body independent of the project team. Lastly, flights are managed in accordance with the rules of the air to guarantee effective management by air traffic authorities.

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